This invention concerns laser scoring of an automotive interior trim piece in which a laser beam is used to score the surface of material, as to create a line of preweakening.
It has previously been proposed to create a preweakening of a trim piece to allow a deployment "door" to be formed by the pressure of an inflating air bag causing an outer covering as a layer of vinyl plastic to rupture in a desired pattern to form an opening allowing the air bag to deploy into the passenger compartment from a storage canister mounted behind the trim piece.
This construction is useful for so-called invisible seam construction installations particularly for the passenger side, in which the location of the air bag is concealed by the absence of any externally perceptible suggestion of a deployment opening door.
The use of the pressure generated by the inflating air bag to rupture the covering skin requires that a precisely controlled preweakening of the covering be carried out.
The air bag must perform reliably over a wide range of ambient temperature conditions. The strength and elongation characteristics of the covering layer, typically of a tough plastic such as vinyl or leather, JPO, TPE, or TPU, varies considerably with ambient temperature. If the covering layer presents too much resistance to rupture, proper deployment of the air bag may not occur due to the resulting delay in overcoming resistance of the covering layer.
At the same time, the preweakened covering must retain sufficient strength so as to not crack or show the line of preweakening on the passenger side.
Covering layers, particularly when made of cast plastic, typically are of irregular thickness due to the inherent lack of precision of the manufacturing process. This variation in thickness makes it difficult to execute preweakening by scoring, as a scored groove of constant depth will result in an erratic preweakening at points along the door pattern since the thickness of the remaining material will vary.
This in turn causes erratic air bag performance due to variations in the precise moment when the air bag will burst through the covering layer.
Production in the automotive field involves large numbers of parts and such air bag system components should desirably have a very low defect rate, i.e., one part per million or less so as to be consistent with current standards.
The object of the present invention is to provide processes and apparatus for precision laser scoring of workpieces which are of varying thickness.